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Tattoos have often been presented

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in popular media as either marks[br]of the dangerous and deviant

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or trendy youth fads.

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But while tattoo styles come and go,

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and their meaning has differed[br]greatly across cultures,

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the practice is as old[br]as civilization itself.

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Decorative skin markings have[br]been discovered in human remains

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all over the world,

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with the oldest found on a Peruvian[br]mummy dating back to 6,000 BCE.

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But have you ever wondered[br]how tattooing really works?

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You may know that we shed our skin,

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losing about 30-40,000[br]skin cells per hour.

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That's about 1,000,000 per day.

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So, how come the tattoo doesn't[br]gradually flake off along with them?

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The simple answer[br]is that tattooing involves

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getting pigment deeper into the skin

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than the outermost layer that gets shed.

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Throughout history, different cultures

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have used various methods[br]to accomplish this.

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But the first modern tattooing machine

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was modeled after Thomas Edison's[br]engraving machine

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and ran on electricity.

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Tattooing machines used today

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insert tiny needles,[br]loaded with dye, into the skin

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at a frequency of 50[br]to 3,000 times per minute.

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The needles punch through the epidermis,

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allowing ink to seep deep into the dermis,

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which is composed of collagen fibers,[br]nerves, glands, blood vessels and more.

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Every time a needle[br]penetrates, it causes a wound

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that alerts the body to begin[br]the inflammatory process,

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calling immune system cells[br]to the wound site

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to begin repairing the skin.

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And it is this very process[br]that makes tattoos permanent.

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First, specialized cells[br]called macrophages

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eat the invading material in an attempt[br]to clean up the inflammatory mess.

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As these cells travel[br]through the lymphatic system,

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some of them are carried back with a belly[br]full of dye into the lymph nodes

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while others remain in the dermis.

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With no way to dispose of the pigment,

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the dyes inside them remain[br]visible through the skin.

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Some of the ink particles[br]are also suspended

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in the gel-like matrix of the dermis,

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while others are engulfed[br]by dermal cells called fibroblasts.

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Initially, ink is deposited[br]into the epidermis as well,

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but as the skin heals, the damaged[br]epidermal cells are shed

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and replaced by new, dye-free cells

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with the topmost layer peeling[br]off like a heeling sunburn.

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Blistering or crusting is not typically[br]seen with professional tattoos

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and complete epidermal[br]regeneration requires 2-4 weeks,

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during which excess[br]sun exposure and swimming

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should be avoided to prevent fading.

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Dermal cells, however,[br]remain in place until they die.

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When they do, they are taken up,[br]ink and all, by younger cells nearby,

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so the ink stays where it is.

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But with time, tattoos do fade naturally

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as the body reacts[br]to the alien pigment particles,

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slowly breaking them down[br]to be carried off

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by the immune system's macrophages.

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Ultraviolet radiation can also[br]contribute to this pigment breakdown,

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though it can be mitigated[br]by the use of sunblock.

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But since the dermal cells[br]are relatively stable,

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much of the ink will remain deep[br]in the skin for a person's whole life.

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But if tattoos are embedded in your skin[br]for life, is there any way to erase them?

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Technically, yes.

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Today, a laser is used[br]to penetrate the epidermis

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and blast apart underlying pigment[br]colors of various wavelengths,

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black being the easiest to target.

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The laser beam breaks the ink globules[br]into smaller particles

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that can then be cleared away[br]by the macrophages.

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But some color inks are harder[br]to remove than others,

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and there could be complications.

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For this reason, removing a tattoo[br]is still more difficult than getting one,

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but not impossible.

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So a single tattoo may[br]not truly last forever,

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but tattoos have been around longer[br]than any existing culture.

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And their continuing popularity means[br]that the art of tattooing is here to stay.